Immersion lithography in wafer scanning

The idea that liquid media enhances imaging performance has been implemented into technology starting in the 19th century, when oil-immersion microscopy was introduced. Nearly two centuries later, immersion principles are now fully integrated into lithography, wherein high-refractive-index liquid fills the lens-wafer gap to enhance imaging capabilities. This innovation supports the mass manufacturing of semiconductor chips that power electronic devices.

In electronics manufacturing, wafers must be rapidly and precisely positioned under the projection lens with minimal mechanical constraints to maximize both imaging fidelity and throughput. Fluid dynamics in immersion lithography thus becomes a necessary consideration. Although the industrial standard has now evolved to confine and stabilize liquid through engineered microfluidic channels, thereby allowing the wafer to be scanned in a dry environment, multiphase flow instabilities still introduce challenges in high-throughput scanning.

Bridging fundamental fluid dynamics and lithography engineering, Yuan et al. reviewed multiphase flow dynamics in wafer defect control, discussing different types of liquid interfacial phenomena.

“We present a unified theoretical framework incorporating the diverse defect origins within the immersion system of immersion lithography into the contexts of gas-liquid and solid-liquid two-phase flows,” said author Zhicheng Yuan. “This enables the convergence of previously disparate research outcomes into the optimization of immersion systems.”

The team hopes that by highlighting unresolved two-phase flow challenges, the scientific community will work to more closely integrate fundamental fluid dynamics and semiconductor manufacturing.

“Such cross-disciplinary attraction is expected to drive the application of novel approaches to defect suppression and ultimately alleviate the current practical challenges of high defect density and low yield improvement in immersion lithography,” said Yuan.

Source: “Multiphase flow challenges in immersion lithography,” by Zhicheng Yuan, Shangpei Dai, Mingyue Hu, and Bin Xu, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0345090 .